AS GROWN LiF : Mn2+ SAMPLES ANALYSED BY LUMINESCENCE

(1)

HAL Id: jpa-00225053

https://hal.archives-ouvertes.fr/jpa-00225053

Submitted on 1 Jan 1985

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished or not. The documents may come from

teaching and research institutions in France or

abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est

destinée au dépôt et à la diffusion de documents

scientifiques de niveau recherche, publiés ou non,

émanant des établissements d’enseignement et de

recherche français ou étrangers, des laboratoires

publics ou privés.

AS GROWN LiF : Mn2+ SAMPLES ANALYSED BY

LUMINESCENCE

F. Rodriguez, M. Moreno

To cite this version:

(2)

JOURNAL

DE

PHYSIQUE

Colloque C7, supplCment au nOIO, T o m e

46,

octobre 1985 page C7-151

AS GROWN L ~ F : M ~ ~ + SAMPLES ANALYSED B Y LUMINESCENCE

F. Rodriguez and M. Moreno

D p t o de Optica y E.M., Facultad de C i e n c i a s , 39005 Santander, Spain

Abstract

-

EvJcJence of the formation of three ~ G e c i ~ i t a t e d phases in as grown LiF: Mn single crystals by qeans of the luminesce ce technique is reported. All phases involve [ M ~ F ~ ]

-

units though the *:lh

-

F distance of one of them is 2.03

A.

This unusual distance has been related to the e- xistence of the Suzuki phase.

I

-

INTRODUCTION

3

Alkali halide crystals doped with weak or moderate concentrations (g10 ppm) of divalent cations can give rise to the formation of microcrystals of precipitated phases /1,2/. In order to have evidences about it and to get some structural informa- tion on the precipitated phases, optical and magnetic techniques can be useful when divalent transition-metal cations are involved. This work shows the usefulness of ths+luminescence technique for analysing samples axtracted from an as grown LiF: Mn single crystal.

11

-

EXPERIMENTAL

Single crystals of LiF doped with MnF2 were grown in inert atmosphere by the Czo- chralski method. Emission and excitation spectra between 10K and room temperature

(RT) were taken using a Jobin-Ivon JY-3D spectrofluorimeter with suitable Oriel filters and an Air-Products close circuit cryostat.

I11

-

RESULTS

In all the analysed samples the only excitation spectrum observed at RT is that of figure 1, the corresponding em3ssion peak being at-660 nm. That spectrum ( S ) can be hnderstood as being due to h4+ in Oh 2ymm&try. The band at 217 nm has been associated to a double excitation T2(G! + TI, E ( G ) , which means that the spectrum cannot be related to isolated Mn 2 t ~ o n s in LiF. Though the position of crystal- -field peaks given in figure 1 are different from that observed for compounds like EbMnF3 or MnF2 an analysis of the e5terimental data sfven in figure 1 and a compa- rison wlth the rsults for KZnF3: Mn 2nd RbCdF3: Mn /3htindicate that this spectrum could also correspond to a [ M ~ F ~ ] complex whose Mn - F- distance, R, is very unusual: R should be 2.03

A,

that is much closer t2+the ~ i +

-

F distance than to 2.13 A corresponding to the sum of ionic rad'i ,of Mn

₁

and F-. This consequence has been derived from the value lODq = 9070 cm- found for spectrum S (fig. I), which is 1500 cm- higher than that for RbMnF3. This experimental results suggest

(3)

JOURNAL

DE

PHYSIQUE

that the S spectrum c n be related to the existence of the Suzuki phase detested in other alkali halides loped with divalent+cationy /1,2/. In that phase the Mn

-

F-

distance can be el~~Se"'t0 that @tween.Li and F because of the presence of nearby vacancies. 'When trdisparentfsamples are cooled another excitation spectrum, called A, is seen besides spectrum S. On figure 2 is4depicted spectrum A taken at 77K. This s p e ~ t r u m ~ c a n also be related to a [M~F~] -fomplex but having a value of R e- qual to 2.15 A as inferred from lODq = 7040 cm corresponding to A./3/

On figure 3 is depicted the evolution of the emission spectrum when temperature goes from 11 to-200K. At 11K, two different emission bands are seen but when temperature is raised the emission peak corresponding to spectrum A goes progressively towards higher wavelengths and its intensity decreases. Above 200K only spectrum S is observed. 'The evolution with LL.III[ICI.II~.U~~ dl nl,l~ryu(l by U ~ U C tru111 A IY ct10ru~Ler~1~- tic of an excitation migration proceses / 4 / . It means&that spectrum A shoyid also be related to a precipitated phase containing

[M~F~.

unlts but with a Mn

-

F- distance about 0.03

A

higher than that for RbMnFg.

Finally in samples with milky aspect, we have observed below-ZOOK a spectrum, called B, different from spectrum A . The evolution of spectrum B with temperature is also characteristic of an excitation migration processes / 4 / . The peak positions suggest that it might be associated to MnF2 rnicrocrystals.

W A V E L E N G T H

( n r n )

(4)

WAVELENGTH I n m )

Fig. 2

(phase

-Excitation A). T = 77K

spectrum corresponding to the transparent zone of .Detected wavelength: 600 nm.

the crystal

6 0 0 7 0 0 8 0 0 W A V E L E N G T H ( n

Fig. 3

-

Evolution of the emissiom spectrum corresponding to phases S and A with temperature. The shift toward higher wavelengths in the A emission band when temperature goes up, means excitation transfer.

Acknowledgements

Thanks are due to J.A.Aramburu and A.Gomez-brefiosa for their help in some measure- ments. This work has been supported by the CAICYT.

REFERENCES

/1/ De Andres, A . , and Calleja, J.M., Solid State Comrnun., 78 (1983) 73.

/2/ Moreno, M., Rodriguez, F., Aramburu, J.A., Jaque, F. anTlopez, F., Phys. Rev.

B

28

(1983) 6100.

/3/ Rodriguez, F. and Moreno, M., J. Chem. Phys., in press.